1. Field of the Invention
This invention relates to an electrophotographic plate. More particularly, it relates to a highly sensitive electrophotographic plate having a photosensitive layer comprising an organic photoconductive material.
2. Description of the Prior Art
Heretofore, inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide have been widely used in the photosensitive layer of the electrophotographic plates. Studies on use of organic photoconductive materials for the photosensitive layer of the electrophotographic plates have been advanced, and some of them have materialized into practical use. The organic photoconductive materials have many advantages over the inorganic materials, for example, they are light in weight, and easy to fabricate as a film, and can be easily manufactured into a photosensitive plate, and into a transparent photosensitive plate depending upon the kinds of the materials. While various studies have been made on the organic photoconductive materials regarding photoconductive polymers represented by polyvinylcarbazole, these polymers are not always satisfactory in view of this film-forming property, flexibility, bondability and the like and they tend to produce cracks or peel off from substrates when formed as a film. Although plasticizer, binder and the like have been added in order to overcome the above-mentioned defects, since such addition is liable to cause another problems such as reduction in the sensitivity and the increase in the residual potential, it has been very difficult to obtain practical photosensitive plates.
On the other hand, while it is easy to prepare photosensitive plates having excellent mechanical properties using low molecular weight-organic photoconductive compounds, since polymers excellent in the film-forming property, flexibility, bondability and the like can be selected as a binder, it has been difficult to find those compounds suitable to the preparation of highly sensitive photosensitive plates.